In recent years, a linear-array semiconductor laser having stripes of active layers formed one-dimensionally has been available in a continuous-wave oscillation type providing a power output of about 50 W. The linear-array semiconductor laser has stripes, which has a width ranging from 100 μm to 200 μm and has one ends thereof formed as emitters, equidistantly arranged on a planar basis at a density of 100 stripes per cm.
As shown in FIG. 2, several linear-array semiconductor lasers stacked in the form of a two-dimensional array are provided, whereby a power output is readily increased. The two-dimensionally arrayed semiconductor laser is referred to as a stacked-array laser diode, and a type of stacked-array laser diode providing a power output of several kilowatts is locally procurable. If a group of laser beams radiated from the stacked-array laser diode can be converged on an optical system and then routed to a fiber bundle through which the group of laser beams is propagated, the stacked-array laser diode can be adopted for a wide range of applications including laser processing.
Assuming that one stacked-array laser diode has N layers, the stacked-array laser diode radiates laser beams (a group of laser beams) numbering a product of about 100 by N. The stacked-array laser diode serves as a light source providing laser beams arranged in the form of a two-dimensional array. Moreover, high-power semiconductor lasers including a quasi-continuous wave (“CW”) semiconductor laser have a number of emitters congested therein. An generated light may be mixed with light emitted from an adjoining emitter immediately after it is emitted, whereby the same number of nearly continuous linear light waves as the number of layers can be provided in parallel with one another.
Each of laser beams (e.g., a stripe light) is emitted from a flat light source. The angle of divergence of a component φ of the laser beam perpendicular to an active layer is large enough so as to range from about 40° to 50°, and the angle of divergence of a component θ thereof horizontal thereto is generally as small as to be about 10°. Hereinafter, a direction perpendicular to the active layer in which the angle of divergence is large shall be called a “fast axis,” and a direction horizontal to the active layer in which the angle of divergence may be called a “small axis.” Each of the stripes has a width that may be as small as 1 μm or less in the fast axis, and each may have a length of about 100 μm in the slow axis are congested. Therefore, the stripes serving as linear light sources respectively may constitute a light source having a width of approximately 10 mm.
Assuming that an ordinary lens or the like is used to converge a group of laser beams emitted from the stacked-array laser diode, the fast-axis components of the laser beams are readily converged to have a diameter of several hundreds of micrometers. However, the slow-axis components thereof are hardly converged to have a diameter of several millimeters. A high power density that is a feature of laser processing is not attained readily. Japanese Unexamined Patent Publication (Kokai) No. 2004-096092, the entire disclosure is incorporated herein by reference, describes a method of using an optical system, which improves the property of convergence of slow-axis components, to drastically reduce the diameter of a spot of a converging light to several hundreds of micrometers or less.
Particular aspects of the conventional systems and methods, and certain problems associated therewith are described in detail below with reference to the accompanying drawings, in comparison with the exemplary embodiments of the present invention.